In a spinning mill, bobbins of cops unwound by a winder are normally returned to the spinning frame side in order to use them again. To this end, various bobbin supply systems have been proposed and put into practical use. Further, it is a very popular means to differentiate bobbins to be supplied to spinning frames from each other in accordance with types of yarns to be set on the spinning frames, for example, to differentiate such bobbins in color, to facilitate discrimination of types of yarns of cops for a next step.
In this manner, it is necessary for a bobbin supply system to supply a predetermined bobbin precisely to a predetermined spinning frame, and a simplest one of conventional bobbin supply systems for realizing such function is constituted such that, for example, a pair of bobbin supply devices B1 and B2 and a plurality of spinning frames S1, S2, . . . , Sm are communicated with each other by way of a single transport passage C (FIG. 5). Here, each of the bobbin supply devices B1 and B2 is constituted such that it forwards a bobbin of a predetermined type into the transport passage C in response to a bobbin requesting signal from a predetermined spinning frame S1 (i=1, 2, . . . , m). Such bobbin requesting signal includes information representative of the spinning frame Si and information which specifies a type of a bobbin requested. It is to be noted that a bobbin change-over mechanism not shown which operates in response to a bobbin requesting signal is incorporated at each of branch points at which the transport passage C branches to the individual spinning frame Si. Thus, a bobbin transported from the upstream side of the transport passage C can be sent into a predetermined spinning frame Si by means of the corresponding change-over mechanism.
Further, m spinning frames S1, S2, . . . , Sm may be divided into two groups individually including k spinning frames and m-k simming frames, and a transport passage C and a pair of bobbin supply devices B1 and B2 may be provided similarly as in the system shown in FIG. 5 for each of the groups (FIG. 6). Such arrangement is advantageous in that the availability factor of the entire spinning frames can be improved because a bobbin supplying operation can be performed simultaneously to two spinning frames Si and Sj (1.ltoreq.i.ltoreq.k, k+1.ltoreq.j.ltoreq.m) which belong to the different groups from each other.
The prior art, however, has a problem that it cannot always be adapted precisely for a demand for lot production of many articles by small quantities which is conducted commonly in recent spinning mills. In particular, since normally the doffing period is different depending upon a type of yarn to be set on a spinning frame, in case various types of yarns are handled in the prior art arrangement shown in FIG. 5, there is the possibility that such an opportunity that a spinning frame having a comparatively short doffing period is rendered inoperative for a bobbin supplying operation for another spinning frame having a comparatively long doffing period may be increased, which will significantly deteriorate the overall availability factor.
On the other hand, while the overall availability factor can be improved as compared with the prior art arrangement shown in FIG. 5 if yarns of the same type are worked on spinning frames which belong to the same group, there is a problem that, since the number of spinning frames involved in each group is fixed, the arrangement cannot cope effectively with a variation in number of production lots of each yarn type.